The present invention relates to sensor circuits, and, more particularly, to an output circuit that outputs a sensor detection signal.
Micromachining technology is used to manufacture sensors for detecting pressure, acceleration, and the like. Micromachining allows for such sensors to be made very small, mass produced, and have a high accuracy. Such a sensor may handle a plurality of parameters (e.g., values for a plurality of coordinate axes). Japanese Laid-Open Patent Publication No. 10-239196 (FIG. 3) describes a low cost interface circuit that has a simple structure. The interface circuit is connected to a capacitive type sensor including two capacitors having variable values. The interface circuit includes an operational amplifier. A sampling capacitor is connected between the output terminal and inverting input terminal of the operational amplifier. A hold capacitor is connected between the non-inverting input terminal of the operational amplifier and a reference voltage source. The inverting input terminal of the amplifier is connected to one end of first, second, and third capacitors. The other end of each of the first and second capacitors is connected to a power supply and the third capacitor is short-circuited. The other ends of the first and second capacitors and the output terminal of the amplifier are each connected to the non-inverting input terminal of the amplifier. Multiple sensors are connected sequentially to the interface circuit via a switching circuit.
Japanese Laid-Open Patent Publication No. 2009-20094 (FIG. 2) describes an acceleration sensor unit that allows for reduction of the chip size. The sensor unit is connected to an acceleration sensor that detects acceleration in each direction of the X, Y, and Z axes. The sensor unit includes a circuit that sequentially generates a temperature coefficient for correcting the acceleration in each of the X, Y, and Z axes directions. The accelerations are corrected sequentially with the corresponding one of the temperature coefficients to generate an acceleration signal.
In the technology described in Japanese Laid-Open Patent Publication No. 10-239196, the same operational amplifier is shared to reduce the chip size. In the technology described in Japanese Laid-Open Patent Publication No. 2009-20094, the same circuit for generating the temperature coefficient is shared to reduce the chip size. However, the output circuit is formed by capacitors that include an analog switch or capacitance. Thus, further reduction in area is required.